The goal of this research is to study the neural mechanisms underlying binaural signal processing in the cat inferior colliculus. The proposal addresses three issues: 1) the mechanism by which high frequency neurons utilize interaural time cues; 2) the relationship between synaptic organization and binaural processing; and 3) the role of descending cortical inputs on binaural response properties. The high frequency studies may provide the neural basis for the observation that human listeners can lateralize complex high frequency signals on the basis of interaural time cues; a finding that has necessitated modification of the classic view that the low and high frequency system use separate localization cues: interaural time and interaural intesity cues, respectively. The purpose of the synaptic organization studies is to determine the neural mechanisms responsible for binaural interactions, and the related ultrastructural components. The rationale of examining cortical influences is the finding that afferents from the ipsilateral auditory cortex project to a specific and division substantial subdivision of the inferior colliculus, viz. the dorsal cortex. Since descending cortical and ascending lemniscal inputs are mixed in this subdivision, the binaural interactions may be different from that in the central nucleus; a division of the inferior colliculus that only receives lemniscal input. To resolve the above issues, we will employ extra and intracellular recordings, acoustical and electrical stimulation, and light and electron microscopic analysis.